670 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1 QO2 1903. 



The idea of an unknown transformation, in space, of radiant light and heat from the sun into 

 another form of energy, seems to have occurred recently to other scientists. 



In a paper, just published, by JULIUS, on the results from the "Netherlands Eclipse Expedition 

 I9i2",( 1 ) the following conclusion is found: 



"Less than j~^ of the total (ultra-violet, visible, and infra-red) solar radiation proceeds from thi><r 

 parts of the celestial body which lie outside the photospheric level. 



"This result proves that it is impossible to maintain the theory which considers the photosphere to 

 be a layer of incandescent clouds, whose decrease of luminosity from the centre toward the limb of the 

 solar disk would be caused by absorption and diffusion of light in an enveloping atmosphere ("the dusky 

 veil"). For if this theory were right, then, according to the calculations made by PICKERING, Wn.sn\ 

 SCHUSTER, VOGEL, SEELIGER and other astrophysicists, such an atmosphere should absorb an important 

 fraction (f to ^) of the sun's radiation. Now, as the fraction emitted appears to be smaller than 

 yet the atmosphere must be in a stationary condition, one would be forced to conclude that the main 

 part of the absorbed energy is continually being dissipated through space in some absolutely un<> ; 

 form. This necessary inference not being acceptable, we must look for another interpretation of the 

 photosphere." 



However this may be, it would be very interesting if the energy of the light and heat 

 could to some extent return to the sun from space. The electric rays possibly reach as far out a 

 light rays, or at any rate exceedingly far, and the greater part of the energy in an electric discharge 

 such as this may gather at the cathode, i. e. on the surface of the sun, where the electric arcs in 

 turn would create new heat for the radiation of more light. 



In this way the age of the sun, which HELMHOLTZ and KELVIN, according to the mechanii 

 theory, put at not more than 50 million years, may perhaps be put at so many hundred million y 

 as geologists, after researches on the earth, absolutely require. There are doubtless other sour 

 reservoirs of energy than those with which we are now acquainted. HELMHOLTZ was not acquainted 

 with radium, for instance, which has of late been made use of to make the sun old enough. 



129. It will be immediately apparent what far-reaching consequences are here built upon our 

 experimental analogies. There seems to be a constantly increasing appreciation of the fruitfulness of tru 

 method established by the representation of such analogies for the study of celestial phenomena. 



In 1860, HUGGINS made a laboratory, where numerous physical experiments were made for the 

 interpretation of astronomical observations. The advantage of imitating the celestial phenomena in labora- 

 tory experiments, a method which forms exactly the base of the present studies, was thus known and 

 appreciated half a century ago. The method has been followed by many, and has of late yielded marvellous 

 results, HALE having discovered the existence of powerful magnetic forces in the solar vortices, and 

 DESLANDRES having in this way made some very interesting experiments on the solar corona. 



The important phenomena, which I have discovered, of disruptive discharges from points on a mag- 

 netic cathode-globe, have especially occupied my attention. 



In order to investigate closely the electric analogies to the vortex-formation about the sun-spots, 

 and to study the wonderful capacity that the globe seems to have in these disruptive discharges, I have 

 recently resumed the whole of my experimental series with an entirely new arrangement, in which a 

 magnetic cathode-globe of 24 cm. diameter could be employed. 



I will here only give a schematic description of these experiments, of which good photographic 

 reproductions are found below. 



(') Koninklijke Akademie van Wetenschappen te Amsterdam, May 23, 1912. 



